Photocatalyst element, method and device for preparing the same

ABSTRACT

A photocatalyst according to the invention comprises a photocatalytic film of a compound of titanium and oxygen and is characterized in that the photocatalytic film is made porous and has 0.02 or higher value as a value calculated by dividing the arithmetical mean deviation of profile Ra with the film thickness. The photocatalytic film can also be specified by the intensity ratio between x-ray diffraction peaks of the anatase structure of titanium oxide. Such a porous photocatalytic material can be obtained by a reactive sputtering method in conditions of adjusting film formation parameters such as the film formation rate, the sputtering pressure, the substrate temperature, the oxygen partial pressure and the like in proper ranges, respectively, and the photocatalyst material is provided with excellent decomposition and hydrophilization capability.

TECHNICAL FIELD

The invention relates to a photocatalyst, a photocatalyst productionmethod, a photocatalyst production apparatus and particularly to aphotocatalyst having a photocatalytic function of promoting generationof active species by light radiation, a photocatalyst production methodand a photocatalyst production apparatus.

BACKGROUND ART

Recently, a photocatalytic thin body using titanium oxide has drawnattraction. “Photocatalyst” is a substance having semiconductivephysical properties, excited when light with energy higher than the bandgap energy between the conduction electron band and charged electronband is radiated, and thereby producing electron-positive hole pairs.

Titanium dioxide with anatase type crystal structure is photo-excited byradiating light with wavelength of 387 nm or shorter and simultaneouslycauses decomposition reaction based on redox reaction and reaction forhydrophilization reaction different from the decomposition reaction(activation). So far, as a metal oxide simultaneously causing these tworeactions, titanium oxide, tin oxide, and zinc oxide have been known andas a metal oxide causing only decomposition reaction, strontium titanateand ferric oxide and as a metal oxide causing only the hydrophilizationreaction, tungsten trioxide have been known, respectively.

Self-washing function, deodorization function, anti-bacterial functionand the like can be provided by utilizing the above-mentioned reactionsand a variety of members and groups of products coated with such aphotocatalyst have been proposed.

As a method for producing such a photocatalyst, various methods such asa binder method, a sol-gel method, and a vacuum evaporation method havebeen proposed.

The binder method involves steps of dispersing finely granular titaniumoxide in a binder having an adhesive property, applying the obtaineddispersion to a predetermined substrate and heating and drying theapplied dispersion. However, the method has a problem that since thefinely granular titanium oxide is buried in the binder, the catalyticfunction tends to be deteriorated.

The sol-gel method is a method for obtaining a photocatalytic film byapplying a liquid-phase agent containing a titanium chelate or atitanium alkoxide containing titanium to a predetermined substrate,drying and then firing the agent at a temperature as high as 500° C. orhigher. However, the method has a problem that since it requires thefiring step at a temperature as high as 500° C. or higher, materialsusable as the substrate are considerably limited in terms of the heatresistance.

Besides these formation methods, formation methods by using a vacuumevaporation method or sputtering method have been proposed.

For example, in JP Patent No. 2,901,550, a photocatalyst having alayered structure of titanium oxide and silicon oxide by a vacuumevaporation method is disclosed.

Also, in Japanese Patent Application Laid-Open No. 2000-126613, a methodfor depositing silicon oxide by reactive sputtering is disclosed.

Meanwhile, on the basis of evaluation results of various physicalproperties of titanium oxide films formed under variously differentconditions by sputtering, the inventors of the invention have found thata titanium oxide film formed under conditions different from those ofconventional methods has a particular structure different fromconventional structures. The inventors have found that with respect tosuch a titanium oxide film, the photocatalytic property is remarkablyimproved as compared with that of a conventional film.

The invention is accomplished based on such findings and an object ofthe invention is to provide a photocatalyst having an excellentphotocatalytic property and simultaneously having a good dark placeretention property and improved productivity, a photocatalyst productionmethod and a photocatalyst production apparatus.

DISCLOSURE OF THE INVENTION

A first photocatalyst of the invention comprises a photocatalytic filmof a compound of titanium and oxygen and is characterized in that thephotocatalytic film is formed to be porous and has 0.02 or higher as avalue calculated by dividing the arithmetical mean deviation of profileRa with the film thickness.

The arithmetical mean deviation of profile Ra of the photocatalytic filmmay be 1.3 nm or more.

A second photocatalyst of the invention comprises a photocatalytic filmof a compound of titanium and oxygen and is characterized in that thephotocatalytic film is formed to be porous and has 5 or less as theintensity ratio of the (101) diffraction peak of the anatase structureof titanium oxide to the (112) diffraction peak of the anatase structureof titanium oxide.

A third photocatalyst of the invention comprises a photocatalytic filmof a compound of titanium and oxygen and is characterized in that thephotocatalytic film is formed to be porous and has 100 or less as theintensity ratio of the (101) diffraction peak of the anatase structureof titanium oxide to the (112) diffraction peak of the anatase structureof titanium oxide.

In all of the above-mentioned photocatalysts, the film thickness of thephotocatalytic film may be not thinner than 40 nm and not thicker than100 nm.

A buffer layer of silicon oxide may further be formed under thephotocatalytic film.

The refractive index of the photocatalytic film may be 2.7 or lower.

A silicon oxide film may be formed on the photocatalytic film.

In that case, the thickness of the silicon oxide film is not thinnerthan 3 nm and not thicker than 7 nm.

A photocatalyst production method of the invention is a method forproducing a photocatalyst comprising a photocatalytic film of a compoundof titanium and oxygen and is characterized by including a step ofdepositing the photocatalytic film at a film formation rate of 0.6 nm/sor lower by sputtering a titanium-containing target in oxygen-containingatmosphere.

The above-mentioned deposition may be carried out at a temperaturesatisfying the following inequality:

R≦2.36 exp(−410(1/T)

where T denotes a temperature of the surface to deposit thephotocatalytic film thereon.

A second photocatalyst production method of the invention is a methodfor producing a photocatalyst comprising a photocatalytic film of acompound of titanium and oxygen and is characterized by including a stepof depositing the photocatalytic film by sputtering atitanium-containing target in oxygen-containing atmosphere at not lowerthan 3 Pa and not higher than 5 Pa.

A third photocatalyst production method of the invention is a method forproducing a photocatalyst comprising a photocatalytic film of a compoundof titanium and oxygen and is characterized by including a step ofdepositing the photocatalytic film by sputtering a titanium-containingtarget in atmosphere containing oxygen not less than 10% and not morethan 30%.

In the first to third photocatalyst production methods, prior to thedeposition of the photocatalytic film, a buffer layer of silicon oxidemay be deposited.

Further, a step of depositing silicon oxide on the photocatalytic filmmay be added.

A photocatalyst production apparatus of the invention is an apparatusfor producing a photocatalyst comprising a photocatalytic film of acompound of titanium and oxygen, the apparatus comprising a first filmformation chamber capable of keeping atmosphere at a reduced pressurelower than the atmospheric pressure; an electric power source forapplying voltage to a target installed in the first film formationchamber; heating means for heating a substrate; a gas introductionmechanism for introducing a reaction gas containing oxygen into thefirst film formation chamber; and a controller capable of controllingthe heating means, and is characterized in that, at the time of formingthe photocatalytic film of a compound of titanium and oxygen bysputtering in the first film formation chamber, the controller controlsthe heating means so as to satisfy the following inequality:

R≦2.36 exp(−410(1/T):

between the film formation rate R of the photocatalytic film and thesurface temperature T of the substrate.

The controller may control the gas introduction mechanism so as to keepthe pressure of the first film formation chamber at not lower than 3 Paand not higher than 5 Pa at the time of forming the photocatalytic filmby sputtering.

Further, the controller may control the gas introduction mechanism so asto keep the oxygen content in the first film formation chamber not lessthan 10% and not more than 30% at the time of forming the photocatalyticfilm by sputtering.

The apparatus may further comprise a heating chamber having the heatingmeans and a transporting mechanism for transporting the substrate fromthe heating chamber to the first film formation chamber, and formationof the photocatalytic film by sputtering maybe carried out after thesubstrate is heated in the heating chamber and then transported to thefirst film formation chamber by the transporting mechanism.

The apparatus may further comprise a second film formation chambercapable of forming a silicon oxide film and is enabled to form a siliconoxide on the substrate prior to the formation of the photocatalytic filmby sputtering.

The apparatus may further comprise a third film formation chambercapable of forming a silicon oxide film and is enabled to form a siliconoxide on the photocatalytic film after the formation of thephotocatalytic film by sputtering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view exemplifying the structure of a photocatalystaccording to an embodiment of the invention.

FIG. 2 is a schematic view showing the surface of a photocatalytic film10.

FIG. 3 is a schematic view exemplifying the cross-sectional structure ofa photocatalyst 10.

FIG. 4 is a schematic view showing the main part configuration of asputtering apparatus employed for experiments.

FIG. 5 is a graph exemplifying the temperature fluctuation of asubstrate 100 during the sputtering.

FIG. 6 is an electron microscopic photograph of the surface of aphotocatalytic film obtained by reactive sputtering.

FIG. 7 is an electron microscopic photograph of the surface of aphotocatalytic film obtained by reactive sputtering.

FIG. 8 is a graph exemplifying the results of a wax decomposition andhydrophilization test of the photocatalytic film 10 of the invention.

FIG. 9 is a graph showing the correlation between the surface roughnessof the photocatalytic film and the contact angle measured by an AFM(Atomic Force Microscopy).

FIG. 10 is a graph formed by plotting the contact angle in relation tothe value Ra/T calculated by dividing the surface roughness Ra with thefilm thickness of each of Samples A to D.

FIG. 11 is a graph showing an x-ray diffraction pattern of thephotocatalytic film of Sample C.

FIG. 12 is a diffraction pattern obtained after removing the backgroundnoise by data processing of the diffraction pattern of FIG. 10.

FIG. 13 is a graph obtained after measuring the x-ray diffractionpattern of the photocatalytic film of Sample A and similarly removingthe background noise from the diffraction pattern.

FIG. 14 is a graph obtained by plotting the refractive index and thedensity ratio in relation to the total pressure.

FIG. 15 is a collective table showing the film formation conditions forphotocatalytic films of Examples carried out by DC sputtering by theinventors.

FIG. 16 is a collective table showing the film formation conditions forphotocatalytic films of Comparative examples carried out by DCsputtering by the inventors.

FIG. 17 is a graph showing the correlation between the oxygen partialpressure at the time of sputtering and the contact angle of the obtainedphotocatalytic film.

FIG. 18 is a graph showing the correlation between the total pressure atthe time of sputtering and the contact angle of the obtainedphotocatalytic film.

FIG. 19 is a graph showing the correlation between the film formationrate at the time of sputtering and the contact angle of the obtainedphotocatalytic film.

FIG. 20 is a graph showing the correlation between the film thickness ofthe photocatalytic film formed by sputtering and the contact angle ofthe obtained photocatalytic film.

FIG. 21 is a flow chart showing the procedure of a wet typedecomposition capability test.

FIG. 22 is a graph exemplifying the results of the wet typedecomposition capability test.

FIG. 23 is a schematic view exemplifying the cross-sectional structureof a photocatalyst having a buffer layer provided thereon.

FIG. 24 is a graph showing the results of the wax decomposition andhydrophilization test.

FIG. 25 is a schematic view showing the cross-sectional structure of aphotocatalyst according to a second embodiment of the invention.

FIG. 26 is a graph exemplifying the results of a wax decomposition andhydrophilization test of a photocatalytic film having a layeredstructure of FIG. 25.

FIG. 27 is a graph exemplifying the results of the wax decomposition andhydrophilization test of the photocatalytic film according to the secondembodiment of the invention.

FIG. 28 is a graph exemplifying the results of the wax decomposition andhydrophilization test of the photocatalytic film according to the secondembodiment of the invention.

FIG. 29 is a graph exemplifying the results of the wax decomposition andhydrophilization test of the photocatalytic film according to the secondembodiment of the invention.

FIG. 30 is a graph showing alteration of a contact angle of thephotocatalytic film of the second embodiment of the invention in thecase wherein the film is kept in a dark place.

FIG. 31 is a graph showing the photocatalytic functions of thephotocatalysts of the invention and Comparative example.

FIG. 32 is a graph showing an x-ray diffraction pattern of Sample D.

FIG. 33 is a graph showing an x-ray diffraction pattern of Comparativeexample 1.

FIG. 34 is a graph for comparison of the photocatalytic functions of thephotocatalysts of the invention and comparative examples.

FIG. 35 is a graph for comparison of the photocatalytic functions of thephotocatalysts of the invention and comparative Example.

FIG. 36 is a schematic view exemplifying the main part configuration ofa photocatalyst production apparatus of the invention.

FIG. 37 is a schematic view exemplifying the main part configuration ofa TiO₂ film formation chamber 230 (or 240).

FIG. 38 is a schematic view showing a modified example of thephotocatalyst production apparatus of the invention.

FIG. 39 is a cross-sectional view of TiO₂ film formation chamber 230 or240 in the vertical direction.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described in details with reference to theaccompanying drawings.

Based on results of the examinations and investigations, the inventorsof the invention have found that the activity can remarkably be improvedif a photocatalytic material such as titanium oxide was made porous.Such a porous photocatalytic material can be obtained by employing areactive sputtering method and considerably increasing the filmformation rate as compared with that in a conventional method and at thesame time properly adjusting film formation parameters such as thesputtering pressure and the substrate temperature in proper ranges andparticular physical properties different from those of a conventionalmaterial can be obtained.

Further, if such a porous photocatalytic material is coated with asilicon oxide with a predetermined film thickness, the surface canefficiently be protected without actual interference of thephotocatalytic function and at the same time the material is providedwith excellent sustainability-in-dark place.

Hereinafter, embodiments of the invention will be described more indetail with reference of concrete examples.

First Embodiment

As a first embodiment of the invention, a porous photocatalytic film andits production method will be described.

FIG. 1 is a schematic view exemplifying the structure of a photocatalystof the embodiment of the invention.

That is, a photocatalyst of the invention comprises a photocatalyticfilm 10 formed in a thin film on a predetermined substrate 100. As thematerial of the photocatalytic film 10, titanium oxide (TiO_(x)) isused, and in the invention, the photocatalytic film 10 of titanium oxideis formed to be porous.

FIG. 2 is a schematic view showing the surface state of thephotocatalytic film 10. That is, the figure shows the surface of thephotocatalytic film of titanium oxide in a film thickness of 135 nm on asubstrate. A large number of granules G with a size of 10 nm or smallerare observed in the surface and these granules are not densely packedbut gaps S are kept among the granules.

FIG. 3 is a schematic view exemplifying the cross-sectional structure ofthe photocatalyst 10. As shown in the figure, the gaps S are formedamong the numberless granules G and a film structure with an extremelyhigh surface area is obtained.

Such a porous photocatalytic film 10 shows a remarkably excellentphotocatalytic function as compared with that of a conventional one.

Hereinafter, the photocatalytic film of the invention will be describedmore in details with reference to its production method.

The photocatalytic film of the invention can be formed by a reactivesputtering method.

FIG. 4 is a schematic view showing the main part configuration of asputtering apparatus employed for experiments. That is, while beingconnected with a cathode 103, a target 102 made of metal titanate isinstalled in the inside of a vacuum chamber 101. On the other hand, asubstrate 100 to deposit the photocatalytic film thereon is installed inan anode 104 side.

At the time of film formation, at first the chamber 101 is evacuated tobe in a vacuum state by a vacuum gas discharge pump 106 and dischargegases of argon (Ar) and oxygen (O₂) are introduced from a gas supplysource 107. An electric field is applied between the anode 104 and thecathode 103 from an electric power source 110 to start plasma discharge108. Subsequently, the surface of the target 102 is sputtered and themetal titanium and oxygen are bonded on the substrate 100 to form atitanium oxide film 10. In this case, the electric power to be loadedfrom the electric power source 110 may be DC (direct current) power orRF (radio frequency) power.

In a concrete example to be described hereinafter, a photocatalytic filmis formed by a DC sputtering method by employing a DC power sourceunless specific remark is given.

Further, at the time of sputtering, the substrate 100 is kept in afloating state relatively to the chamber 101 (at a ground potential).

As it will be described later, in such a sputtering apparatus, aphotocatalytic film with a predetermined film quality can be obtained byadjusting the electric power loaded for plasma discharge, the pressureand the composition of the ambient gas at the time of sputtering, andthe temperature of the substrate.

The temperature of the substrate 100 is confirmed by sticking athermo-label 109 to the substrate.

FIG. 5 is a graph exemplifying the temperature fluctuation of thesubstrate 100 during the sputtering. Here, the substrate temperaturefluctuation from a room temperature to the temperature at the time ofstarting sputtering is shown for the film formation conditions A to C.The respective conditions are as follows.

Oxygen Loaded DC Deposition Total partial Condition electric power ratepressure pressure A 2 kW 18 nm/min 1 Pa 30% B 2 kW 22 nm/min 3.5 Pa  30% C 3 kW 36 nm/min 5 Pa 30%

As can be seen from FIG. 5, in the case of starting sputtering at a roomtemperature as the substrate temperature, the temperature of thesubstrate 100 tends to be increased with the lapse of time owing to theheat radiation from the sputtering source and reaches a saturatedtemperature depending on the loaded electric power.

The saturated temperature depends on mainly the loaded electric powerand in the case where the electric power is 2 kW, it is about 230° C.and in the case where the electric power is 3 kW, it is about 300° C.

Incidentally, the deposition of the thin film is sometimes finishedbefore the temperature reaches the saturated temperature. For example,the deposition rate of Condition C is 36 nm/min and it takes 3 minutesand 45 seconds to form a titanium oxide film with a film thickness of135 nm, so that the highest substrate temperature in the case ofstarting the deposition from the room temperature is about 230° C. Onthe other hand, before sputtering, the substrate may be heatedpreviously for degassing treatment and the sputtering may be started ina state at a temperature higher than a room temperature. In such a case,since the temperature increases close to the saturated temperature fromthe raised state, in the case of previous heating to a high temperature,the temperature may be decreased toward the saturated temperature duringthe deposition in some cases.

FIGS. 6 and 7 are electron microscopic photographs of the surfaces ofphotocatalytic films obtained by such reactive sputtering. That is,these FIGS. 6( a) to 6(d) and FIGS. 7( a) to 7(d) are surfacephotographs of respective Samples A to D of titanium oxide films.

FIGS. 6 and 7 are photographs of a single sample with differentmagnifications and the length of the bars in the right bottom of therespective photographs is equivalent to 300 nm in FIGS. 6 and 119 nm inFIG. 7.

Sample A, Sample B, and Sample C are formed in the above-mentionedCondition A, Condition B, and Condition C, respectively. Each of Samplesis obtained by depositing titanium oxide as a photocatalytic film on aSiO₂ butter layer on a silicon wafer used as the substrate 100 and thefilm thickness of titanium oxide 10 is 135 nm for Samples A to C and 50nm for Sample D.

From FIGS. 6 and 7, the surface of Sample A has a structure in whichfine particles are closely agglomerated and the particles are denselypacked.

On the other hand, in the surfaces of Samples B to D, numberlessparticles with a diameter of about 10 nm or smaller are observed,however they are not densely packed and kept from one another at gaps.That is, they are formed to be porous.

That the particles of Sample D are smaller than those of Samples B and Cis supposedly greatly attributed to the difference of the filmthickness.

The photocatalytic function of the photocatalytic film 10 obtained insuch a manner was evaluated by “wax decomposition hydrophilizationtest”. The test is for evaluating both of “decomposition function” and“hydrophilization function” together among photocatalytic functionswhich the photocatalytic film 10 has. The “decomposition function” is afunction of decomposing an organic material such as a wax by activeoxygen species such as hydroxy radical and superoxide formed in thesurface of the photocatalytic film. The “hydrophilization function” is afunction of improving the hydrophilicity of the surface of thephotocatalytic film. The contents of the wax decompositionhydrophilization test carried out by the inventors are approximately asfollows.

(1) Making the surface of the photocatalytic film 10 hydrophilic bywashing with a neutral detergent.

(2) Applying a solid wax to the surface of the photocatalytic film 10and drying the wax at a room temperature for 1 hour. The solid wax usedin this case is Hero (trade name, manufactured by SurLuster Inc.) ofmainly carnauba wax.

(3) Washing the surface of the photocatalytic film 10 with a neutraldetergent and then drying the surface at 50° C.

(4) Measuring the contact angle of water droplet formed on the surfaceof the photocatalytic film 10 periodically by continuously radiatingblack light beam (BLB). The wax formed on the surface of thephotocatalytic film 10 is decomposed by the photocatalytic function byradiation of black light beam. In the state that the wax remains on thesurface, the contact angle of the water droplet is high, however whenthe wax is decomposed, the contact angle of the water droplet becomessmall.

Accordingly, it can be said that the photocatalytic function is moreactive as the decomposition is promoted more even if the radiationintensity of the black light beam is small or the contact angle of thewater droplet is smaller after a predetermined duration of radiation.

FIG. 8 is a graph exemplifying the results of the wax decomposition andhydrophilization test of the photocatalytic film 10 of the invention.Here, the data of Sample D described in description of FIGS. 5 to 7 isshown. The graph is formed by plotting the data obtained by changingradiation intensity of black light beam to be 500 μW/cm², 50 μW/cm², and10 μW/cm².

The radiation intensity, 500 μW/cm², is close to the condition of a waxdecomposition hydrophilization test which is commonly carried out andthe radiation intensity, 50 μW/cm², is rather slight intensity, and theradiation intensity, 10 μW/cm², is extremely slight intensity.

From FIG. 8, the contact angle is about 83 degrees before the blacklight beam radiation, meanwhile in the case of the radiation intensityof 500 μW/cm² and 50 μW/cm², the contact angle is sharply decreased assoon as black light beam is radiated and after 1 hour, it is decreasedto about 9 degrees, after 2 hours, to about 5 degrees, and after 10hours, to about 3 degrees and accordingly, it is understood that the waxis quickly decomposed.

Also, a further remarkable point is that the photocatalytic function isobtained even by the light radiation as ultra slight of 10 μW/cm² lightradiation intensity. That is, although the contact angle decrease speedis moderate, after 3 hours, the contact angle is decreased to about 56degrees, after 6 hours, to about 22 degrees, and after 12 hours, toabout 4 degrees. As it will be described later, as compared with that ofa conventional photocatalytic film, it is a remarkable characteristic ofthe photocatalytic film of the example that the photocatalytic functionis obtained even by such an ultra slight light radiation.

The inventors of the invention formed photocatalytic films with variousfilm qualities by variously adjusting the film formation conditions inthe reactive sputtering method and evaluated the formed films.Hereinafter, relations between the physical properties of aphotocatalytic film and the film formation parameters will be describedsuccessively.

At first, as one of parameters defining the “porosity” of aphotocatalytic film, “surface roughness” of the film was investigated.

FIG. 9 is a graph showing the correlation between the surface roughnessof the photocatalytic film and the contact angle measured by an AFM(Atomic Force Microscopy). That is, the axis of abscissa of the figureshows the surface roughness Ra of the photocatalytic film of titaniumoxide. The axis of ordinate of FIG. 9 shows the contact angle of waterdroplet after 1-hour radiation of black light beam (radiation intensity500 μW/cm²) in the wax decomposition hydrophilization test similar tothat described above.

Four samples A to D plotted in FIG. 9 are respectively same as Samples Ato D described in relation to FIGS. 5 to 8.

From FIG. 9, in the case where the surface roughness Ra of thephotocatalytic film (Sample A) is about 0.9 nm, the contact angle isfound extremely high as about 83 degree, even if black light beam isradiated for 1 hour. On the other hand, in the case where the surfaceroughness Ra is 1.3 nm (Sample D), the contact angle is drasticallydecreased to 9 degrees in the same condition, in the case where thesurface roughness Ra is 3.5 nm (Sample B), the contact angle isdecreased to about 8 degrees, and in the case where the surfaceroughness Ra is 3.65 nm (Sample C), the contact angle is decreased toabout 8 degrees.

In other words, it can be understood that if the surface roughness Ra ishigher than 1 nm, the photocatalytic function is sharply improved.

With respect to the relations among the film formation condition, thefilm thickness, and the surface roughness, the following relations canbe obtained.

Deposition Total Film Surface Sample rate pressure thickness roughness A18 nm/min 1 Pa 135 nm 0.9 nm B 22 nm/min 3.5 Pa   135 nm 3.5 nm C 36nm/min 5 Pa 135 nm 3.65 nm  D 36 nm/min 5 Pa  50 nm 1.3 nm

That is, the surface roughness Ra is increased mainly by increasing the“deposition rate” and the “total pressure”. From the surface photographsof FIGS. 6 and 7, as described, it is found that the “gaps” among“particles” tend to be wide as the surface roughness Ra is higher.

Incidentally, as described in details in Examples, the deposition ratesof Samples B to D are about 10 times as high or more than as comparedwith that in the case of photocatalytic film formation by a conventionalreactive sputtering.

In other words, if the deposition rate is considerably increased ascompared with that in a conventional case and the parameters such as thetotal pressure and the substrate temperature are adjusted as describedabove, a porous photocatalytic film can be obtained. The film thicknessof Samples B to D is in a range of a common film thickness as aphotocatalytic film. Accordingly, if the surface roughness Ra is higherthan 1.3 nm, it is supposed that a porous thin film having an excellentphotocatalytic function can be obtained.

The reason for that the surface roughness Ra of Sample D is smaller thanthat of Sample C formed in the same film formation condition is becausethe film thickness is different. Accordingly, with respect to the dataof FIG. 9, normal distribution of the surface roughness Ra in relationto the film thickness is plotted.

FIG. 10 is a graph formed by plotting the contact angle in relation tothe value Ra/T calculated by dividing the surface roughness Ra with thefilm thickness of each of Samples A to D.

As it is understood from the figure, Ra/T of Sample A was about 0.0062and Ra/T of Samples B to D was in a range of 0.026 to 0.027 and thusRa/T was divided into two groups. In the case of the former (Sample A),the contact angle is as high as about 83 degrees after 1-hour radiationof black light beam, meanwhile in the case of the latter (Samples B toD), the contact angle is found drastically decreased to about 7 to 9degrees.

If a range of 30 degrees or lower is defined to be the allowable rangeof the contact angle after 1-hour radiation of black light beam in theinvention, it can be understood that the ratio of the surface roughnessto the film thickness, that is, Ra/T should be 0.02 or higher. If arange of 10 degrees or lower is defined to be the allowable range in theinvention, it can be understood that the ratio of the surface roughnessto the film thickness, that is, Ra/T should be 0.02r or higher.

Accordingly, in the invention, the density of a photocatalytic film tobe formed can be lowered and a porous photocatalytic film comprisingfine particles and having gaps among the particles can be formed byconsiderably increasing the deposition rate and adjusting the totalpressure and the substrate temperature. It is found that such a porousphotocatalytic film can drastically be improved in the photocatalyticproperties if the surface roughness exceeds a predetermined value.

The reason for the activation of the photocatalytic function by increaseof the porosity is supposedly attributed to that the surface area of thephotocatalytic film is increase by making the film porous and defectsadvantageously functioning for the photocatalytic function are properlyintroduced into the vicinity of the surface of the particles.

According to the invention, since the film formation is carried out at aremarkably increased deposition rate as compared with that in aconventional case, the film formation time can considerably be shortenedas an advantageous point. For example, in the case of forming aphotocatalytic film with a film thickness of 200 nm, it conventionallytakes 100 minutes, that is, 1 hour and 40 minutes, as the depositiontime, meanwhile it can be shortened to be 10 minutes or shorter. As aresult, the production throughput of the photocatalytic film canremarkably be improved and the cost can be lowered.

Further, according to the invention, since the film formation can becarried out at a lower substrate temperature than that of a conventionalformation, the requirements for the heat resistance of a substrate canconsiderably be moderated. That is, various materials, e.g. organicmaterials such as plastics with low heat resistance, which cannot beused conventionally, can be usable and the application range of thephotocatalytic film can remarkably be widened.

Hereinafter, a variety of the properties of the photocatalytic film ofthe invention can be described in relation to the film formationparameters.

FIG. 11 is a graph showing an x-ray diffraction pattern of thephotocatalytic film of the above-mentioned sample C.

From the figure, it can be understood that the background level israther high and the diffraction peak of TiO₂ is weak and broad. In otherwords, it can be assumed that the crystal is rather disordered and thecrystal grains are also rather small and contain a large number ofdefects.

FIG. 12 is a diffraction pattern obtained after removing the backgroundnoise by data processing of the diffraction pattern of FIG. 11. Thediffraction peak appearing in the figure corresponds to the diffractionpeak of TiO₂ having an anatase structure and it is found that higherreflection is obtained.

FIG. 13 is a graph obtained after measuring an x-ray diffraction patternof the photocatalytic film of the above-mentioned sample A and removingthe background noise from the diffraction pattern.

From FIG. 13, the diffraction peak of TiO₂ with an anatase structure isalso obtained, however in comparison with FIG. 12 (Sample C), thebalance of the height of the appearing reflection peaks is founddifferent. More particularly, for example, with respect to the intensityof another diffraction peak to the (101) diffraction peak of anataseappearing in the vicinity of the diffraction angle, 25 degrees, therelative intensity of the main peak is rather high in Sample A (FIG. 13)as compared with that in Sample C (FIG. 12).

The relative intensity ratios of the (101) diffraction peak to othermain diffraction peak intensities are collectively shown below.

Intensity ratio of diffraction peak Sample A Sample C (101)/(112) 10.43.8 (101)/(200) 7.5 3.7 (101)/(105) 6.3 2.2 (101)/(204) 10.7 3.9(101)/(215) >300 9.6

From the above intensity ratio, the intensity ratios of the (101)diffraction peak of Sample A are overwhelmingly high and it can beunderstood that a thin film structure oriented in [110] direction isobtained. In comparison with that, in the case of Sample C, it canquantitatively be understood that the intensity ratios of the (101)diffraction peak are extremely low. That is, in Sample C, suchorientation is low and accordingly, it can be assumed that agglomeratesof a large number of crystal grains having disordered orientationrelations are formed.

Also from the x-ray diffraction data, in the invention, it can beunderstood that since a photocatalytic film is deposited at a highspeed, a high pressure, and a low temperature as compared with those ina conventional case, a porous thin film having a large number of defectsis formed. Attributed to such a particular porous structure, thephotocatalytic function is supposedly improved remarkably.

In consideration of the results (FIGS. 9 and 10) of the waxdecomposition hydrophilization test, it is supposed to be desirable thatthe intensity ratio of the (101) diffraction peak to the (112)diffraction peak is about 5 or lower, the intensity ratio of the (101)diffraction peak to the (105) diffraction peak is about 4 or lower, andthe intensity ratio of the (101) diffraction peak to the (215)diffraction peak is about 100 or lower.

Next, the dependency of the film quality on the total pressure at thetime of sputtering will be described.

That is, a titanium oxide film was deposited in the condition that theloaded electric power and the oxygen partial pressure are fixed at 2 kWand 30%, respectively, at the time of sputtering and the refractiveindex and the density ratio were measured. The results are shown asfollows.

Total pressure Refractive index N Density ratio 1 Pa 2.73 1 2 Pa 2.690.94 3 Pa 2.63 0.88 5 Pa 2.3 0.829

The above-mentioned refractive index was measured by an elipsometerusing helium-neon (He—Ne) laser. The density ratio was evaluated byeffective solute approximation of the spectroscopic elipsometer.

FIG. 14 is a graph obtained by plotting the refractive index and thedensity ratio in relation to the total pressure.

As it can be understood from the graph, if the total pressure isincreased at the time of film formation, it is found that both of therefractive index and the density tend to be gradually decreased. That issupposedly attributed to the reflection of the tendency that the filmquality of the porous photocatalytic film becomes coarser as the totalpressure is increased more.

Separately, the composition of the photocatalytic film and the absolutevalue of the density of Sample B (film formed at the total pressure of3.5 Pa) were measured by Rutherford back scattering analysis (RBS). Themeasurement conditions are as follows.

Energy decomposition capability 24 keV Impinging energy 2.0 MeVImpingent angle 0 degree Impinging ion 4 He⁺ Impinging beam diameter 1.0mm Sample current 10 nA

The following results are obtained for Sample B by the RBS measurement.

O/Ti 2.02 Density 4.45 g/cm³.

The measurement precision of the O/Ti value is about ±5% and themeasurement precision of the density is also about ±5%.

It is supposed that excellent photocatalyst properties as describedabove can be obtained by forming a photocatalytic film porous equal toor more than Sample B, that is decreasing the density. In other words,from the above-mentioned measurement results, if the density of thephotocatalytic film is adjusted to be 4.45 g/cm³ in the invention, aporous photocatalytic film excellent in the photocatalytic function canbe obtained.

Next, the relation of the film formation conditions at the time ofsputtering and the photocatalytic film properties will be described. Theinventors of the invention formed a photocatalytic film by variouslychanging the conditions of the reactive sputtering carried out by usingthe above-mentioned DC sputtering apparatus and investigated theproperties of formed films.

FIG. 15 is a collective table showing the film formation conditions ofthe photocatalytic films of Examples carried out by DC sputtering by theinventors.

Also, FIG. 16 is a collective table showing the film formationconditions of the photocatalytic films of Comparative examples carriedout by DC sputtering by the inventors.

That is, in this case, relations between the parameters of the “oxygenpartial pressure (%)”, the “total pressure (Pa)”, the “film formationrate (nm/second)”, the “temperature (° C.) ”, and the “film thickness(nm)” and the properties of the formed photocatalytic films wereinvestigated.

Here, the temperature at the time of sputtering is the averagetemperature during the sputtering after a substrate is heated previouslyin a preliminary chamber and then transported to a sputtering chamber.Argon (Ar) was used as a carrier gas at the time of sputtering.

As the evaluation method for the photocatalytic films, the waxdecomposition hydrophilization test was carried out and those having acontact angle of water droplet 10 degree of lower after 1-hour radiationof black light beam with luminance of 500 μW/cm² were regarded asqualified and those having a contact angle higher than 10 degree wereregarded as unqualified.

The effect of the oxygen partial pressure on the photocatalytic film atthe time of sputtering will be described.

FIG. 17 is a graph showing the correlation between the oxygen partialpressure at the time of sputtering and the contact angle of the obtainedphotocatalytic film. That is, the axis of abscissa of the figure showsthe oxygen partial pressure at the time of the reactive sputtering andthe axis of ordinate shows the contact angle of water droplet after1-hour radiation of black light beam (radiation intensity 500 μW/cm²) inthe wax decomposition hydrophilization test.

All of Samples plotted in FIG. 17 were formed by deposition in theconditions of the total pressure of 5 Pa, DC loaded electric power of 2kW, the film formation speed of 0.3 nm/second, the temperature of 330°C., and the film thickness of 50 nm at the time of sputtering.

From FIG. 17, it can be understood that the contact angle is extremelylow and remarkably excellent photocatalytic function can be obtained inthe condition that the oxygen partial pressure is in the range of notlower than 10% and not higher than 30% at the time of sputtering. On theother hand, if the oxygen partial pressure is too low or too high, thecontact angle is increased.

That is supposedly attributed to that both of the cases that the oxygenpartial pressure is too low and too high at the time of sputtering, theoxygen content in the obtained photocatalytic films is out of a properrange or that the bonding state of the metal element and oxygen becomesinstable.

Further, based on the observation, the inventors found that thephotocatalytic film formed in the condition that the oxygen partialpressure was not higher than 10% was not transparent but opaque having ametallic color. It implies that since the oxygen partial pressure is toolow, the oxygen content of the obtained photocatalytic film isinsufficient.

On the other hand, if the oxygen partial pressure is controlled to be ina range not lower than 10% and not higher than 30% at the time ofsputtering, the obtained photocatalytic film becomes transparent andexcellent photocatalytic properties can be obtained. It is supposedlyattributed to that the oxygen content in the photocatalytic film is in aproper range, the bonding state of the metal element and oxygen becomesstable, the life time of electron-positive hole pairs excited in thefilm by light radiation is prolonged and consequently the photocatalyticfunction is activated.

Next, the effect of the total pressure on the photocatalytic film at thetime of sputtering will be described.

FIG. 18 is a graph showing the correlation between the total pressure atthe time of sputtering and the contact angle of the obtainedphotocatalytic film. That is, the axis of abscissa of the figure showsthe total pressure at the time of the reactive sputtering and the axisof ordinate shows the contact angle of water droplet after 1-hourradiation of black light beam (radiation intensity 500 μW/cm²) in thewax decomposition hydrophilization test.

All of the samples plotted in FIG. 18 were formed by deposition in theconditions of the oxygen partial pressure of 30%, the film formationspeed of 0.3 nm/second to 0.6 nm/second, the temperature of 330° C., andthe film thickness of 50 nm at the time of sputtering.

From FIG. 18, it can be understood that the contact angle of waterdroplet is about 14 degree at the total pressure 2 Pa at the time ofsputtering and the contact angle is decreased to about 4 degree when thetotal pressure becomes 3 Pa and it implies that excellent decompositionand hydrophilization properties are obtained. It is supposedlyattributed to that if the total pressure is too low, the practicaloxygen supply amount is decreased and the film quality of thephotocatalytic film does not become “porous” as shown in FIG. 2 or FIG.3.

Meanwhile, in the case of the total pressure at 5 Pa, the contact angleis as low as about 4 degrees, but in the case where the total pressureis increased to 6Pa, the contact angle is sharply increased to about 86degrees. It is supposedly attributed to that if the total pressure istoo high, the film quality of the photocatalytic film and the bondingstate of the metal element and oxygen are changed.

From these results, it can be understood that excellent photocatalyticproperties can be obtained by adjusting the total pressure to be in arange not lower than 3 Pa and not higher than 5 Pa at the time ofsputtering.

Next, the effect of the film formation rate at the time of sputtering onthe photocatalytic film will be described.

FIG. 19 is a graph showing the correlation between the film formationrate at the time of sputtering and the contact angle of the obtainedphotocatalytic film. That is, the axis of abscissa of the figure showsthe film formation rate of the photocatalytic film at the time of thereactive sputtering and the axis of ordinate shows the contact angle ofwater droplet after 1-hour radiation of black light beam (radiationintensity 500 μW/cm²) in the wax decomposition hydrophilization test.

The samples plotted in FIG. 19 were formed by deposition in theconditions of the oxygen partial pressure of 30%, the total pressure 3to 5 Pa, the temperature of about 330° C., and the film thickness of 40to 100 nm at the time of sputtering.

From FIG. 19, it can be understood that in the case where the filmformation rate is in a range of 0.2 to 0.6 nm, the contact angle ofwater droplet is 10 degrees or lower and the excellent photocatalyticfunction is obtained. When the film formation rate is increased to 0.7nm/second, the contact angle is increased to about 17 degrees. It issupposedly attributed to that if the film formation rate is too high,the film quality of the photocatalytic film and the bonding state of themetal element and oxygen are deteriorated.

From the results, it can be understood that the film formation rate ispreferably at least 0.2 nm/second and at highest 0.6 nm/second.

On the other hand, the film formation rate significantly affects the“throughput” at the time of production. For example, in the case where a50 nm-thick photocatalytic film is deposited, if the film formation rateis controlled to be 0.2 nm/s, the time taken for the film formation is250 second, that is, exceeds 4 minutes. Meanwhile, if the film formationrate is controlled to be 0.4 nm/s, the time taken for the film formationcan be shorten to be a half, that is, 125 second (about 2 minute). Asdescribed, in terms of the productivity, the film formation rate isdesired to be high, as high as approximately 0.4 nm/second or higher.

Next, the effect of the temperature at the time of sputtering on thephotocatalytic film will be described.

The inventors paid attention to the correlation between the“temperature” and the “film formation” rate at the time of sputtering.From data shown collectively in FIGS. 15 and 16, the followingapproximation inequality between the “temperature T” and the “filmformation rate R” is extracted so as to obtain a “qualified” film, thatis, the contact angle of water droplet after 1-hour radiation of blacklight beam is 10 degree or lower.

R2.36 exp(−410(1/T)   (1)

That is, if the photocatalytic film is formed by sputtering in thecondition that the “temperature T” is in the range satisfying theabove-mentioned inequality in relation to the film formation rate R,“qualified” photocatalytic properties can be obtained. Theabove-mentioned inequality (1) can be explained qualitatively asfollows.

That is, at the time of reactive sputtering, the metal element sputteredfrom the target and oxygen molecule supplied form the ambient gas fly tobe adsorbed in the deposition surface of the substrate. These elementsare migrated (transferred) in the deposition surface and then bondedwith each other and fixed in predetermined lattice sites. A portion ofthe energy needed for migration of these metal element and oxygen in thedeposition surface is supplied by heating the substrate.

In the case where the film formation rate is high, since the supplyspeeds of the metal element and oxygen flying to the deposition surfaceare increased, it becomes highly possible that they are fixed at thesites in an incomplete bonding state before they are sufficientlymigrated on the surface. Accordingly, it is required to fix them atstable sites in a properly bonded state by promoting the migration onthe surface by increasing the substrate temperature. Therefore, in thecase where the film formation rate R is high, it is desirable toincrease the substrate temperature T.

In the invention, the photocatalytic film having the excellentphotocatalytic function can be obtained by setting the temperature to bein a range so as to satisfy the above-mentioned inequality (1).

Next, the effect of the film thickness on the photocatalytic film willbe described.

FIG. 20 is a graph showing the correlation between the film thickness ofthe photocatalytic film formed by sputtering and the contact angle ofthe obtained photocatalytic film. That is, the axis of abscissa of thefigure shows the film thickness of the photocatalytic film and the axisof ordinate shows the contact angle of water droplet after 1-hourradiation of black light beam (radiation intensity 500 μW/cm²) in thewax decomposition hydrophilization test.

The samples plotted in FIG. 20 were deposited in the conditions of theoxygen partial pressure of 30%, the total pressure 3 to 5 Pa, thetemperature of about 330° C., and the film formation rate of 0.34 to 0.4nm/second at the time of sputtering.

From FIG. 20, in the case where the film thickness of the photocatalyticfilm is 20 nm, the contact angle is as very high as about 65 degrees,and in the case where the film thickness is 30 nm, the contact angle isdecreased to about 18 degrees. In the case where the film thickness isincreased to 40 nm, the contact angle is decreased to as low as about 6degrees and it can be understood that the excellent photocatalyticfunction is obtained. On the other hand, with respect to the upper limitof the film thickness, so far to the evaluation range, the excellentphotocatalytic function can be obtained until the film thickness isincreased to 170 nm. In other words, the film thickness is better to be40 nm or thicker.

The inventors carried out a wet decomposing capability test in order toinvestigate the relation between the film thickness and the“decomposition function” between the “decomposition function” and the“hydrophilization function” of the photocatalytic film. As an object dyeto be decomposed, Methylene Blue (C₁₆H₁₈N₃S.Cl) is used. Methylene Blueis an organic dye which is scarcely decomposed by UV ray andirreversibly decomposed by decomposition reactivity of the photocatalystto be colorless and therefore, it can be used for the decomposingcapability evaluation of the photocatalytic film.

FIG. 21 is a flow chart showing the procedure of the wet typedecomposition capability test.

At first, as described in step S1, a specimen of a titanium oxide filmis washed with purified water, a surfactant, and ultrasonic washing ifnecessary. Further, after the washing, UV ray with wavelength of 360 nmand an intensity of 1 mW/cm² or higher is radiated for 24 hours orlonger to the specimen by a black light fluorescent lamp to decomposestains of organic matters remaining even after the washing by thephotocatalytic function.

Next, as described in step S2, Methylene Blue is saturated and adsorbedon the surface of the specimen. That is, in order to cancel thefluctuation of the spectra owing to the adsorption of Methylene Blue onthe surface of the specimen, Methylene Blue is previously adsorbed onthe surface to the extent of the saturated amount. The concentration ofMethylene Blue to be used in form of an adsorption solution is adjustedto be 0.02 mmol/l. A new adsorption solution is brought into contactwith the specimen for 12 hours and the adsorption process is repeateduntil the absorbance of the adsorption solution is not decreased.

On completion of the saturated adsorption of Methylene Blue on thesurface of the specimen in such a manner, as described in step S3, aninitial absorption spectrum is measured. In this case, the concentrationof the Methylene Blue test solution is adjusted to be 0.01 mmol/l.

Next, in step S4, the spectrum after light radiation is measured. Thatis, while being put in a cell, the Methylene Blue test solution isbrought into contact with the surface of the specimen and in such asituation, UV ray with 1 mW/cm² is radiated for 20 minutes. Immediatelyafter the light radiation, the absorption spectrum of the Methylene Bluetest solution is measured. Then the measured test solution is quicklyturned back to the cell and while being brought into contact with thespecimen, the solution is subjected to UV radiation again for 20minutes.

In such a manner, the absorption spectrum of the Methylene Blue testsolution is measured after the UV radiation for at every 20 minutes andthe measurement is carried out 9 times for radiation duration in total 3hours. Methylene Blue is more quickly decomposed and decolored as thedecomposition capability of the photocatalytic film is higher.Consequently, the absorption property is decreased.

FIG. 22 is a graph exemplifying the results of the wet typedecomposition capability test. That is, in the figure, the axis ofabscissa shows the film thickness of the photocatalytic film and theaxis of ordinate shows the decomposition capability index (nmol/l/min)calculated on the basis of absorbance.

As it can be understood from the figure, the decomposition capabilityindex of the photocatalytic film is increased as the film thickness isincreased and when the film thickness reaches 100 nm, the index isapproximately saturated. That is, in terms of the “decompositionfunction”, the decomposition property of the photocatalytic filmobtained by the sputtering method is found approximately saturated inthe case where the film thickness is in a range of 100 nm or thicker.

In the wax decomposition hydrophilization test shown in FIG. 20, basedon the fact that the excellent photocatalytic function is obtained evenin the case where the film thickness is in a range of 100 nm or thinner,in this film thickness range, it can be assumed that the“hydrophilization property” of the photocatalytic film is functioning.

Further, based on the observation of the inventors, if the filmthickness of the photocatalytic film exceeds approximately 80 nm, doubleimages owing to light reflection are observed in some cases by eyeobservation. Accordingly, from that viewpoint, the film thickness of thephotocatalytic film is desirably adjusted to be in a range of notthinner than 40 nm and not thicker than 80 nm. Also, from the viewpointof throughput, the film thickness of the photocatalytic film isdesirably made thin.

Next, the function of a “buffer layer” to be formed in the substrate andthe photocatalytic film will be described.

FIG. 23 is a schematic view exemplifying the cross-sectional structureof a photocatalyst having a buffer layer.

That is, a buffer layer 50 is formed on a predetermined substrate 100and a photocatalytic film 10 is formed thereon. As a material for thebuffer layer 50, for example, silicon oxide can be employed.

Formation of such a buffer layer 50 can prevent impurity contaminationfrom the substrate 100 to the photocatalytic film 10. Further, theformation can improve the surface state of the substrate 100 and makesthe initial stage of the deposition of the photocatalytic film 10controllable.

For example, in the case where soda-lime glass is used as the substrate100, if the alkali element such as sodium (Na) contained in the glass isdiffused in the photocatalytic film 10, the photocatalytic propertiesare sometimes deteriorated. In such a case, the impurity diffusion canbe prevented and the deterioration of the photocatalytic properties canbe prevented by forming the buffer layer 50 of silicon oxide or thelike.

Also, in the case where the surface of the substrate 100 has unevensurface in micro order, the surface unevenness can be moderated and theinitial stage of the deposition of the photocatalytic film 10 can bemade closer to the ideal state by forming the buffer layer 50 in aproper thickness.

The inventors investigated the effect of the buffer layer 50 by usingsoda-lime glass as the substrate 100, silicon oxide as the buffer layer50, and titanium oxide as the photocatalytic film 10.

FIG. 24 is a graph showing the results of the wax decomposition andhydrophilization test. That is, the axis of abscissa of the figure showsthe radiation duration of black light beam (radiation intensity 500μW/cm²) and the axis of ordinate shows the contact angle of waterdroplet.

In the figure, the results of photocatalysts in which the thickness ofthe buffer layer 50 is adjusted to be 0 nm, 20 nm, 50 nm, 100 nm, and260 nm are shown. Incidentally, with respect to all of the samples, thedeposition of the photocatalytic film 10 was carried out by reactivesputtering and the conditions were adjusted as follows: the oxygenpartial pressure of 30%, the total pressure of 5 Pa, the temperatureabout of 330° C., the film formation speed of 0.5 nm/second, and thefilm thickness of 50 nm.

From FIG. 24, it is found that in one hand, the contact angle of waterdroplet is 50 degrees or higher after 1-hour radiation of black lightbeam in the case where the film thickness of the buffer layer 50 is in arange from zero to 20 nm, on the other hand, the contact angle of waterdroplet is decreased to about 14 degrees after 1-hour radiation in thecase where the film thickness of the buffer layer 50 is 50 nm. Further,in the case where the film thickness of the buffer layer 50 is 100 nm,the contact angle of water droplet is decreased to about 10 degreesafter 1-hour radiation, and in the case where the film thickness of thebuffer layer 50 is 260 nm, the contact angle of water droplet isdecreased to about 4 degrees after 1-hour radiation.

As described, if the buffer layer 50 having a proper thickness isformed, the photocatalytic properties are found improved.

Second Embodiment

Next, as a second embodiment of the present invention, a photocatalystin which a coating layer of silicon oxide is formed on a photocatalyticfilm of titanium oxide or the like having a photocatalytic function willbe described.

FIG. 25 is a schematic view showing the cross-sectional structure of thephotocatalyst of this embodiment.

That is, the photocatalyst of the embodiment has a structure having aphotocatalytic film 10 provided on a substrate 100 and a coating layer20 having further formed thereon. Here, the photocatalytic film 10 is aporous layer similar to the photocatalytic film 10 of titanium oxide orthe like described with reference to FIGS. 1 to 24. Further, as thecoating layer 20, for example, oxides such as silicon oxide can beemployed.

The coating layer 20 properly protects the surface of the photocatalyticfilm 10 to the extent that photocatalytic function is not interfered andat the same time has a function of keeping hydrophilicity. That is, inthe state that light is radiated, as described with reference to FIGS. 1to 24, the porous photocatalytic film 10 exhibits the activephotocatalytic function and decomposes adhering substances to keep highhydrophilicity. However, in the state that no light is radiated, nophotocatalytic function of the photocatalytic film 10 is obtained.Meanwhile, the coating layer 20 keeps the hydrophilicity, and therefore,an effect of preventing fixation of pollutants on the surface can bemaintained.

Accordingly, if the thickness of the coating layer 20 is too thick, thelayer causes interference to the photocatalytic function of thephotocatalytic film 10 and on the other hand, if the coating layer 20 istoo thin, the hydrophilicity becomes insufficient.

FIG. 26 is a graph exemplifying the results of a wax decomposition andhydrophilization test of the photocatalytic film having a layeredstructure shown in FIG. 25. As the substrate 100, soda-lime glass wasused. As the photocatalytic film 10, a titanium oxide film produced inthe same conditions as those for the above-mentioned sample D in thefirst embodiment was used. Meanwhile, as the coating layer 20 to bedeposited thereon, silicon oxide was used. The deposition of the coatinglayer 20 was carried out continuously from the deposition of thephotocatalytic film 10 by reactive sputtering by using a gas mixture ofargon (Ar) and oxygen (O₂). The DC loaded electric power was 300 W: thetotal pressure was 3.5 Pa: and the oxygen partial pressure was 30%.

FIG. 26 shows plotted data of 5 kinds of samples having the coatinglayers 20 with the thickness of 0 nm, 3 nm, 5 nm, 7 nm, and 14 nm,respectively. From the figure, it can be understood that the contactangle in the initial state before black light beam radiation isdecreased in all of Samples having the coating layers 20 as comparedwith that in the sample having no coating layer 20. It means that thecoating layer 20 improves the hydrophilicity of the surface.

On the other hand, on the basis of the contact angle after the blacklight beam radiation, in the case where the thickness of the coatinglayer 20 is 3 nm to 7 nm, the wax decomposition property approximatelysame as that of a sample having no coating layer (the sample with 0 nmthickness of SiO₂) is observed, and therefore, it can be understood thatthe photocatalytic function is scarcely interfered. Incidentally, theradiation intensity of the black light beam employed here is 50 μm/cm².Considering that the intensity is lower than that employed commonly inthe case of carrying out the wax decomposition hydrophilization test asdescribed above, it can be said that the coating layer with thethickness in the above-mentioned range does not practically interferethe photocatalytic function.

However, if the thickness of the silicon oxide layer 20 becomes 14 nm,the decreasing degree of the contact angle becomes small and it meansthe photocatalytic function is interfered.

In other words, from the results shown in FIG. 26, the thickness of thecoating layer 20 is preferable not thinner than 3 nm and not thickerthan 7 nm.

FIGS. 27 to 29 are graphs exemplifying the results of the waxdecomposition and hydrophilization test of the photocatalytic film ofthe embodiment. With respect to the photocatalytic film employed here, atitanium oxide film same as Sample D described in the first embodimentwas used as the photocatalytic film 10 and a silicon oxide film with athickness of 7 nm was used a the coating layer 20.

As Comparative example, data of a sample having no coating layer 20 isalso shown.

FIG. 27 shows data obtained in the case where the radiation intensity ofblack light beam is 500 μm/cm². With this radiation intensity, thephotocatalytic film of the embodiment having the coating layer 20 isfound having better hydrophilicity before and after the radiation.

FIG. 28 shows data obtained in the case where the radiation intensity ofblack light beam is as slight as 50 μm/cm². With this radiationintensity, the photocatalytic film of the embodiment is found havingbetter hydrophilicity before the radiation and approximately samehydrophilicity as that of Comparative example after the radiation.

On the other hand, FIG. 29 shows data obtained in the case where theradiation intensity of black light beam is as extremely slight as 10μm/cm². With this radiation intensity, the photocatalytic film of theembodiment is found having better hydrophilicity after 7 hours from theradiation. It is supposedly attributed to that the hydrophilicity of thecoating layer 20 is dominant to the photocatalytic function of thephotocatalytic film 10 in the ultra slight light radiation.

As described above, according to the embodiment, excellenthydrophilicity can be maintained before the light radiation or in thecase where the light intensity is slight.

FIG. 30 is a graph showing the alteration of the contact angle of thephotocatalytic film of the embodiment in the case where thephotocatalytic film is kept in a dark place.

That is, in this case, the figure shows the results of the measurementof the alteration of the contact angle of the photocatalytic film keptfrom the light and placed in a dark place after the contact angle isdecreased to approximately zero by radiating black light beam.

From the results shown in the figure, in the case where no coating layer20 is formed, the contact angle is increased in a relatively short timeby shutting out the light and is increased to about 45 degrees after 8days. On the other hand, in the case of samples of the embodiment havingthe coating layers 20, the increase of the contact angle is moderate andit is found that as the thickness of the coating layers 20 becomesthicker, the increase is suppressed more. In other words, it isconfirmed that as the thickness of the coating layers 20 becomesthicker, the photocatalytic film is more excellent in the hydrophilicityretention property in a dark place.

As described above, according to the embodiment, formation of thecoating layer 20 with a thickness in a predetermined range on thephotocatalytic film 10 of titanium oxide or the like provides theexcellent retention property in a dark place without causing practicalinterference to the photocatalytic function. As a result, both in thecase of radiating light and in the case of shutting light or radiatingonly extremely slight light, hydrophilicity of the surface can be kepthigh.

Herein after, the embodiments of the invention will be described more indetails with reference to Examples.

Example 1

At first, as Example 1 of the invention, a photocatalyst of the firstembodiment of the invention was produced and compared with Comparativeexample produced by a conventional method.

FIG. 31 is a graph showing the photocatalytic functions of thephotocatalysts of the invention and the Comparative example. That is,this figure shows the results of the wax decomposition hydrophilizationtest and in this case, the radiation intensity of black light beam wasadjusted to be 500 μm/cm².

The photocatalyst of this example of the invention was the same asSample D described as the photocatalytic film of the first embodiment ofthe invention. Comparative examples 1 and 2 were also produced by areactive sputtering method and their properties were also plottedtogether.

The film formation conditions for the respective cases are collectivelyshown as follows

Comparative Comparative Sample D example 1 example 2 Film formation DCsputtering RF sputtering RF sputtering method Loaded electric 3 kW 220 W220 W power Deposition rate 36 nm/min 3.5 nm/min 3.5 nm/min Totalpressure 5 Pa 2.7 Pa 2.7 Pa Oxygen partial 30% 11% 50% pressureSubstrate 280° C. or lower 300° C. 400° C. temperature

Since the above-mentioned sample D was subjected to heating anddegassing in a preliminary chamber before the deposition by sputtering,the initial temperature at the time of deposition was higher than a roomtemperature. However, the deposition was carried out in the conditionthat the highest level of the temperature did not exceed 280° C. duringthe deposition. Further, in all of the samples, the background pressurein the vacuum chamber was decreased by evacuation to 8×10⁻⁴ Pa or lowerbefore the film formation.

From the results shown in FIG. 31, the contact angle before the blacklight beam radiation was 75 degrees for the invention (Sample D), 85degrees for Comparative example 1, and 90 degrees for Comparativeexample 2. When black light beam was radiated, the contact angle wassharply decreased in the photocatalytic film of the invention anddecreased to about 9 degrees after 1 hour. Meanwhile, the decreasingspeed of Comparative examples 1 and 2 was moderate and the contactangles of Comparative examples 1 and 2 were decreased only to 36 degreeand 51 degree, respectively. As described, the photocatalytic film ofthe invention was confirmed to have a remarkable photocatalytic functionas compared with the photocatalytic films of Comparative examples.

The surfaces of these Comparative examples 1 and 2 had structures inwhich the particles 10 times as large as those shown in FIGS. 6( a) and7(a) were densely agglomerated and thus they were not porous.

Next, these samples were subjected to the measurement of the x-raydiffraction pattern.

FIG. 32 is a graph showing the x-ray diffraction pattern of Sample D.

Also, FIG. 33 is a graph showing the x-ray diffraction pattern ofComparative example 1.

The diffraction peaks appearing in these Figs. corresponded to thediffraction peaks of TiO₂ with “anatase structure”.

In comparison of FIG. 32 (Sample D) and FIG. 33 (Comparative example 1),it was found that the intensity of the diffraction peaks relative to thebackground level and the balance among peaks were significantlydifferent although the measurement was carried out in the sameconditions. That is, in Comparative example 1 (FIG. 33), the intensityvalues of the diffraction peaks were extremely high to the backgroundlevel and sharp and outstanding diffraction peaks appeared. Moreover,other than the diffraction peaks at lower order (101) and (200), thediffraction peaks scarcely appeared.

On the contrary, in Sample D of the invention (FIG. 32), the intensitylevels of the diffraction peaks relative to the background level werelow as a whole and slight and broad diffraction peaks were obtained.Moreover, a large number of higher order diffraction peaks appeared.

Based on the investigation of the intensity balance of other diffractionpeaks to the anatase-derived (101) diffraction peak, in the case ofComparative example 1 (FIG. 32), the intensity levels of (101) and (200)diffraction peaks were overwhelmingly high, and accordingly it can beunderstood that a structure strongly oriented in these lower level planedirections was obtained

On the other hand, in the case of Sample D of the invention (FIG. 32),the intensity balance of the (101) diffraction peak was rather low and alarge number of higher level diffraction peaks were observed. That is,in Sample D of the invention, the orientation degree was low and it issupposed that a large number of fine crystal particles with disorderedplane orientation were gathered together.

The intensity ratio of the (101) diffraction peak to other maindiffraction peaks are collectively shown as follows.

Intensity ratio of Comparative diffraction peak Sample D example 1(101)/(112) 3.7 >1,000 (101)/(105) 6.3 approximately 270

From the above intensity ratios, it can be understood that in the caseof the Comparative example 1, the intensity ratio of the (101)diffraction peak was overwhelmingly high and a strongly oriented thinfilm structure was obtained. In comparison therewith, with respect toSample D, it can quantitatively be understood that the intensity ratioof the (101) diffraction peak was extremely low.

In other words, from these results, it is found that the photocatalyticfilm of Comparative example 1 had rather good crystallinity, meanwhileSample D of the invention was porous, had a large number of crystaldefects, and comprised agglomerates of fine particles.

In comparison of the film formation conditions of the invention to thoseof Comparative example, the deposition ratio of the invention was atleast 10 times high and the total pressure was also high and thesubstrate temperature was low. In other words, in these Comparativeexamples, the film formation was carried out at higher temperatures, thelower pressure, and the lower rate. In general, in the case ofdepositing a thin film at a high temperature and a low rate, thecrystalline tends to be good and the film quality tends to be dense.They are coincident with the results of the surface structure and thex-ray diffraction.

On the contrary, in the invention, the deposition rate was considerablyquickened as compared with that of a conventional case and filmformation was carried out at a higher pressure and a lower temperature,so that the photocatalytic film was made to be particularly porous andthe photocatalytic function was remarkably improved.

Example 2

Next, as Example 2 of the invention, the photocatalyst of the secondembodiment of the invention and a conventional photocatalyst werecompared with each other and investigated on the photocatalytic functionunder slight light radiation.

At first, as the photocatalyst of the invention, the same one shown inFIG. 25 was produced. Here, soda-lime glass was used as the substrate100 and a 50 μm-thick buffer layer of silicon oxide was depositedthereon and a photocatalytic film 10 and a coating layer 20 werecontinuously deposited further thereon.

With respect to the photocatalytic film 10, the same one as theabove-mentioned sample B in the first embodiment was deposited. As thecoating layer 20, a 7 nm-thick silicon oxide was deposited by reactivesputtering.

On the other hand, as Comparative example 3, a 100 nm-thick titaniumoxide film was deposited on the same substrate by vacuum evaporation andbuffer layer by vacuum evaporation and a 15 nm-thick silicon oxide filmwas deposited further thereon by vacuum evaporation. At the time of thetitanium oxide deposition, Ti₂O₃ was used as a evaporation source, andwhile oxygen was introduced into the vacuum chamber so as to keep theoxygen partial pressure of 1.3×10⁻² Pa, electron beam evaporation wascarried out. The titanium oxide deposition rate was 18 nm/min and thesubstrate temperature was 200° C.

At the time of silicon oxide deposition, SiO₂ was used as theevaporation source and while oxygen was introduced into the vacuumchamber so as to keep the oxygen partial pressure of 2.6×10⁻² Pa,electron beam evaporation was carried out. The titanium oxide depositionrate was 30 nm/min and the substrate temperature was 200° C.

FIG. 34 is a graph for comparison of the photocatalytic functions of thephotocatalysts of the invention and Comparative example. That is, thefigure shows the results of the wax decomposition hydrophilization testand the radiation intensity of the black light beam was made to be asslight as 50 μm/cm².

It can be understood from FIG. 34 that the contact angles of the initialstate of both of the invention and Comparative example are same, about17.4 degrees, the decreasing rates differ after radiation of black lightbeam. The photocatalyst of the invention showed the contact angledecreased to about 4 degrees after 1-hour radiation, meanwhile thephotocatalyst of Comparative example showed the contact angle decreasedonly to about 11 degrees.

Accordingly, the photocatalyst of the invention was found having a highphotocatalytic function as compared with the photocatalyst having aconventional layered structure even under light radiation as slight as50 μm/cm². It is supposedly attributed to that the photocatalytic film10 was excellent in the photocatalytic function in combination with thatthe film thickness of the coating layer 20 was set in a proper range.

Example 3

Next, as Example 3 of the invention, the photocatalyst of the secondembodiment and a conventional photocatalyst were compared with eachother and investigated on the photocatalytic functions under ultraslight light radiation.

Also in this example, as the photocatalyst of the invention, the sameone shown in FIG. 25 was produced. That is, soda-lime glass was used asthe substrate 100 and a 50 μm-thick buffer layer of silicon oxide wasdeposited thereon and a photocatalytic film 10 and a coating layer 20were continuously deposited further thereon.

With respect to the photocatalytic film 10, the same one as theabove-mentioned sample D in the first embodiment was deposited. As thecoating layer 20, a 7 nm-thick silicon oxide was deposited by reactivesputtering.

On the other hand, as Comparative example 3, the same sample asdescribed above in Example 2 was produced.

FIG. 35 is a graph for comparison of the photocatalytic functions of thephotocatalysts of the invention and Comparative example. That is, thefigure shows the results of the wax decomposition hydrophilization testand the radiation intensity of the black light beam was made to be asultra slight of 10 μm/cm².

It can be understood from FIG. 35 that the contact angle was scarcelydecreased and slightly fluctuated even if black light beam was radiatedin the sample of Comparative example 3. It means the photocatalyticfunction was scarcely caused by the black light beam radiation as ultraslight of 10 μm/cm².

On the other hand, the contact angle of the photocatalyst of theinvention was reliably decreased by black light beam radiation eventhough the decrease was slight and it was found the photocatalyticfunction was caused.

Accordingly, the photocatalyst of the invention was found having a highphotocatalytic function even under light radiation as ultra slight of 10μm/cm² and as compared with that of a photocatalyst having aconventional layered structure, the photocatalytic function was active.It is also supposedly attributed to that the photocatalytic film 10 wasexcellent in the photocatalytic function in combination with that thefilm thickness of the coating layer 20 was set in a proper range.

Example 4

Next, as Example 4 of the invention, a production apparatus preferableto be used for producing a photocatalyst of the invention will bedescribed.

FIG. 36 is a schematic view exemplifying the main part configuration ofa photocatalyst production apparatus of the invention. FIG. 36( a) showsthe plane structure and the FIG. 36( b) shows the cross-sectionalstructure.

Practically, the production apparatus of the invention has a structurecomprising a SiO₂ film formation chamber 210, a heating chamber 220, aTiO₂ film formation chamber 230, a TiO₂ film formation chamber 240, aSiO₂ film formation chamber 250, and a load lock part 260 arranged inthis order above a main chamber 200 which can be vacuum-evacuated.

A transportation table 400 is installed in the main chamber 200 and asubstrate 100 is made rotatable and transportable to the positions underthe respective chambers while being set on the transportation table 400.As shown in FIG. 36( a), when the substrate 100 is transported under therespective chambers by the transportation table 400, it is properlylifted up by an elevating mechanism 600. For example, as shown in FIG.36( b), when the substrate 100 is transported under the TiO₂ filmformation chamber 230, it is lifted up together with a substrate holder420 by the elevating mechanism 600 and transferred to the inner space ofthe film formation chamber 230.

In the case of the production apparatus of the concrete example, thesubstrate 100 introduced into the chamber from the load lock part 260 issuccessively transported by the transportation table 400; a buffer layer50 is formed in the SiO₂ film formation chamber 210; the resultingsubstrate is heated to a predetermined temperature in the heatingchamber 220; a TiO₂ film (photocatalytic film) 10 with a predeterminedthickness is formed in the TiO₂ film formation chambers 230 and 240;further a SiO₂ film 20 is formed in the SiO₂ film formation chamber 250;and then the obtained substrate is taken out of the load lock part 260.

In the heating chamber 220, the substrate 100 can be heated to apredetermined temperature by lamp heating using, for example, a quartzlamp.

FIG. 37 is a schematic view exemplifying the main part configuration ofthe TiO₂ film formation chamber 230 (or 240). In the film formationchamber, a titanium (Ti) target 102 is installed and reaction gases suchas argon and oxygen are made to be introduced through mass flowcontrollers (MFC) 600 and 610.

The substrate holder 420 does not completely seal the film formationchamber 230 and an aperture (not illustrated) is properly formedtherebetween. That is, the film formation chamber 230 isvacuum-evacuated by a vacuum evacuation system connected to the mainchamber 200 through the aperture.

As a reaction gas containing oxygen, for example, argon and oxygen arerespectively introduced into the film formation chamber 230 through theMFCs 600 and 610 and voltage is applied from a DC power source 510 tothe target to carry out reactive DC sputtering.

In this example, the operation of the heating mechanism such as the lampinstalled in the heating chamber 220 is made controllable by acontroller 500. Specifically, as described with reference to FIGS. 15and 16, the control is carried out so as to satisfy the relation of thefilm formation rate R and the substrate temperature T as the followinginequality:

R≦2.36 exp(−410(1/T)   (1).

For example, at the time of producing a photocatalyst, a predeterminedfilm formation rate is inputted in the controller 500. The controller500 then computes the temperature range so as to satisfy theabove-mentioned inequality (1) and previously determines the heatingconditions in the heating chamber to carry out preliminary heating so asto keep the temperature range at the time of film formation.

Also as described with reference to FIGS. 15 and 16, in order to producean excellent photocatalyst, it is desirable to control the totalpressure in a range from 3 Pa to 5 Pa and the oxygen partial pressurenot lower than 10% and not higher than 30%. Accordingly, the controller500 may be made capable of controlling the MFCs 600 and 610 so as tosimultaneously satisfy the above-mentioned conditions.

The film formation rate is mainly determined by the loaded power fromthe DC power source 510, and besides, it is affected by the totalpressure and the oxygen partial pressure, the controller 500 may be madecapable of controlling the MFCs 600 and 610 in consideration of sucheffects.

Since the fluctuation of the substrate temperature during the filmformation differs depending on the loaded power from the DC power source510, the controller 500 is capable of controlling the heating mechanisminstalled in the heating chamber 220 in consideration of this point.

Further, the controller 500 may control the DC power source 510. Thatis, the controller 500 may control the electric power to be loaded intothe target from the DC power source 510 so as to obtain a predeterminedfilm formation rate.

Furthermore, the film formation temperature may be determined prior butnot the film formation rate be determined and inputted prior. That is, afilm formation temperature is previously appointed and the controller500 may compute the film formation rate so as to satisfy theabove-mentioned inequality (1) at the film formation temperature andcontrols the DC power source 510.

Alternatively, neither the film formation rate nor the film formationtemperature is previously set and the controller may properly determinethem to carry out film formation. Also in this case, the controller 500determines the film formation rate and the film formation temperature soas to satisfy the above-mentioned inequality (1) and carries out filmformation.

As described above, according to this example, a photocatalyst havingexcellent photocatalytic properties can stably be produced with a highreproductivity by properly determining and controlling the relationbetween the film formation rate and the film formation temperature.

FIG. 38 is a schematic view showing a modified example of aphotocatalyst production apparatus of the invention. The figure shows aplane structure of the production apparatus and the apparatus has astructure comprising a vertical SiO₂ film formation chamber 210, aheating chamber 220, a TiO₂ film formation chamber 230, a TiO₂ filmformation chamber 240, a SiO₂ film formation chamber 250, and a loadlock part 260 arranged in this order around a transportation mechanism700.

The transportation mechanism 700 has radial holders 720 capable ofsetting a substrate, rotating in the direction shown as the arrow A andtransporting the substrate in the direction show as the arrow B.

FIG. 39 is a cross-sectional view of the TiO₂ film formation chamber 230or 240 in the vertical direction. Same symbols are assigned to the samecomponents described above with reference to FIG. 37 and thereforedetailed description will be omitted with respect to this figure.

The substrate 100 set on the substrate holder 720 is rotated andtransported to the front of a chamber by the transportation mechanism700 and further transported toward the chamber and air-tightly enclosedin the chamber by the holder 720. In such a state, the film formationchamber 230 (240) is vacuum-evacuated by a turbo molecular pump (TMP)110. The transportation space by the transportation mechanism 700 isalso kept in a vacuum state by a vacuum evacuation system which is notillustrated.

In the film formation chamber 230 (240), argon and oxygen are introducedto carry out reactive sputtering. At that time, in the same manner asdescribed relevant to FIG. 37, the film formation rate and the filmformation temperature are controlled by the controller 500 so as tosatisfy the above-mentioned inequality (1). For example, in the casewhere the film formation rate is previously appointed, the controllercomputes the heating conditions of the substrate so as to satisfy theabove-mentioned inequality (1) in the film formation rate and controlsthe operation of the heating mechanism installed in the heating chamber220 to heat the substrate. In the case of this modified example, thecontroller 500 may be capable of controlling not only the heatingmechanism but also the DC power source 510. In this case, the controller500 controls the DC power source 510 to carry out film formation of theTiO₂ film.

As described above with reference to FIGS. 15 and 16, in order toproduce an excellent photocatalyst, it is preferable to control thetotal pressure in a range from 3 Pa to 5 Pa and the oxygen partialpressure not lower than 10% and not higher than 30%. Accordingly, thecontroller 500 may carry out control so as to simultaneously satisfy theabove-mentioned conditions.

Also the production apparatus of this modified example can stablyproduce a photocatalyst having excellent photocatalytic properties witha high productivity by properly determining and controlling the relationbetween the substrate heating condition and the film formation rate bythe controller 500.

Incidentally, in FIGS. 36 to 39, concrete examples of previously heatingthe substrate 100 in the heating chamber 220 installed separately fromthe film formation chamber are described.

However, the invention is not limited to these examples. For example,same effects can be achieved by similarly applying the invention in aproduction apparatus comprising substrate heating mechanisms installedin the film formation chambers 230 and 240. In the case of such aproduction apparatus, the controller 500 may control the substrateheating mechanisms so as to satisfy the above-mentioned inequality (1)and carry out the film formation.

While the invention has been described with reference to the concreteexamples, the description is illustrative of the invention and is not tobe construed as limiting the invention.

For example, as the photocatalytic film of the invention, it is notlimited to titanium oxide (TiO₂), and similar effects can be obtained byusing those obtained by adding predetermined elements to titanium oxideand they are included the scope of the invention.

In the case of forming the photocatalytic film of the invention bysputtering, the reaction gas to be introduced into the chamber is notlimited to argon and oxygen, and for example, it may be a gas mixture ofoxygen and gas other than argon and a gas mixture of argon, oxygen andanother gas.

INDUSTRIAL APPLICABILITY

As described above in details, according to the invention, aphotocatalyst excellent in the photocatalytic function can be providedby forming a particularly porous photocatalytic film differently from aconventional one.

The photocatalyst can maintain the hydrophilicity at a high level evenin a dark place without deteriorating the photocatalytic function bydepositing a silicon oxide film with a predetermined thickness.

Moreover, according to the invention, since the photocatalytic film isformed at a remarkably higher deposition rate than that of aconventional one, the production throughput is greatly improved and theproductivity is improved to considerably lower the cost.

Further, an object coated with the photocatalyst of the invention may beany if its surface is coated with the photocatalyst of the invention andit may include various materials such as a rearview mirror, a body, andwindow glass for an automobile; a variety of mirrors for a bath room andthe like; an outer wall material for a building; an inner wall materialfor a bath room; a toilet stool; a sink; a signpost, and externalmaterials of various displays.

In the case of application to a rearview mirror for an automobile, aclear visible field and safety can be obtained owing to the droppingfunction of droplets and fogging-preventing function of thephotocatalytic film. Also, in the case of application to an automotivebody, a signpost, and an outer wall material of a building,self-cleaning function by rainfall can be obtained.

Consequently, the invention provides a highly capable photocatalyst at alow cost and supplies a variety of coated bodies by its application inmarkets and thus greatly contributes in industrial fields.

1-15. (canceled)
 16. A photocatalyst production apparatus for producinga photocatalyst comprising a photocatalytic film of a compound oftitanium and oxygen, the apparatus comprising: a first film formationchamber capable of keeping atmosphere at a reduced pressure lower thanthe atmospheric pressure; an electric power source for applying voltageto a target installed in the first film formation chamber; heating meansfor heating a substrate; a gas introduction mechanism for introducing areaction gas containing oxygen into the first film formation chamber;and a controller capable of controlling the heating means and the gasintroduction mechanism, wherein, at the time of forming thephotocatalytic film of a compound of titanium and oxygen on thesubstrate by sputtering in the first film formation chamber, thecontroller controls the gas introduction mechanism so as to keep thepressure of the first film formation chamber at not lower than 3 Pa andnot higher than 5 Pa and to keep the oxygen content in the first filmformation chamber not less than 10% and not more than 30%, and controlsthe heating means so as to satisfy the following inequality:R≦2.36 exp(−410(1/T) between a film formation rate R of thephotocatalytic film and a surface temperature T of the substrate at aformation rate not lower than 0.2 nm/s and not higher than 0.6 nm/s. 17.The photocatalyst production apparatus according to claim 16, whereinthe electric power source is a DC power source.
 18. The photocatalystproduction apparatus according to claim 16, wherein the controllercontrols so as to make a film thickness of the photocatalyst not thinnerthan 40 nm and not thicker than 100 nm.
 19. The photocatalyst productionapparatus according to claim 16, further comprising: a heating chamberhaving the heating means; and a transporting mechanism for transportingthe substrate from the heating chamber to the first film formationchamber, wherein the substrate can be transported to the first filmformation chamber by the transporting mechanism after the substrate isheated in the heating chamber to carry out the formation of thephotocatalytic film by sputtering.
 20. The photocatalyst productionapparatus according to claim 19, further comprising a second filmformation chamber capable of forming a silicon oxide film, wherein asilicon oxide can be formed on the substrate prior to the formation ofthe photocatalytic film by sputtering.
 21. The photocatalyst productionapparatus according to claim 19, further comprising a third filmformation chamber capable of forming a silicon oxide film, wherein asilicon oxide can be formed on the photocatalytic film after theformation of the photocatalytic film by sputtering.
 22. A photocatalystproduction apparatus, comprising: a first film formation chamber capableof keeping atmosphere at a reduced pressure lower than the atmosphericpressure; an electric power source for applying voltage to a targetinstalled in the first film formation chamber; heating means for heatinga substrate; a gas introduction mechanism for introducing a reaction gascontaining oxygen into the first film formation chamber; and acontroller capable of controlling the heating means, wherein, at thetime of forming a photocatalytic film of a compound consisting oftitanium and oxygen on the substrate by sputtering in the first filmformation chamber, the controller controls the heating means so as tosatisfy the following inequality:R≦2.36 exp(−410(1/T)) between a film formation rate R of thephotocatalytic film and a surface temperature T of the substrate,wherein the photocatalytic film is an agglomerate of a number of grains,is formed to be porous including gaps among the number of grains at asurface of the photocatalytic film, and has 0.02 to higher value as avalue calculated by dividing the arithmetical mean deviation of profileRa with a film thickness, and the film thickness of the photocatalyticfilm is not thinner than 40 nm and not thicker than 100 nm, thephotocatalytic film is made of titanium oxide formed by the sputtering,and the titanium oxide has 100 or less value as the intensity ratio of a(101) diffraction peak of the anatase structure of titanium oxide to a(215) diffraction peak of the anatase structure of titanium oxidemeasure using a Kα1 characteristic X-ray of copper.
 23. Thephotocatalyst production apparatus according to claim 22, wherein thecontroller controls the gas introduction mechanism so as to keep thepressure of the first film formation chamber at not lower than 3 Pa andnot higher than 5 Pa at the time of forming the photocatalytic film bysputtering.
 24. The photocatalyst production apparatus according toclaim 22, wherein the controller controls the gas introduction mechanismso as to keep the oxygen content in the first film formation chamber notless than 10% and not more than 30% at the time of forming thephotocatalytic film by sputtering.
 25. The photocatalyst productionapparatus according to claim 22, further comprising: a heating chamberhaving the heating means; and a transporting mechanism for transportingthe substrate from the heating chamber to the first film formationchamber, wherein the substrate can be transported to the first filmformation chamber by the transporting mechanism after the substrate isheated in the heating chamber to carry out the formation of thephotocatalytic film by sputtering.
 26. The photocatalyst productionapparatus according to claim 25, further comprising a second filmformation chamber capable of forming a silicon oxide film, wherein asilicon oxide can be formed on the substrate prior to the formation ofthe photocatalytic film by sputtering.
 27. The photocatalyst productionapparatus according to claim 25, further comprising a third filmformation chamber capable of forming a silicon oxide film, wherein asilicon oxide can be formed on the photocatalytic film after theformation of the photocatalytic film by sputtering.